He was born in Philadelphia, Pennsylvania on February 19, 1965 and grew up in Syracuse, New York.

Fishman had a passion for the drums from an early age, and emulated John Bonham, the drummer for Led Zeppelin. He went to Moses Dewitt High School in Syracuse, and after graduation in 1983, he went to the University of Vermont for one year.
He then left with guitarist Trey Anastasio for Goddard College, where he wrote his thesis on "A Self-Teaching Guide to Drumming in Retrospect."

Fishman was one of the bands original members when it formed in 1983, and the band was in fact named after him (he is commonly referred to as Fish). Other than drumming, he also sang back-up vocals and occasionally lead-vocals. He was well-known on tour for his vacuum cleaner solos and his distinctively-patterned dress. Recently, it has been revealed by Anastasio that Fishman is in fact the Wolfman's Brother, a character in a Phish song on the album Hoist.

Fishman also played the drums in a side-project, the band Pork Tornado , with guitarist Dan Archer, saxophonist Joe Moore, keyboardist Phil Abair, and bassist Aaron Hersey.